This invention relates generally to electronic devices that incorporate a vacuum packaged microelectronic device. More particularly, the present invention relates to an electronic device having a non-evaporable getter material disposed on the same substrate as the active transistors and other logic devices.
The ability to maintain a vacuum for a prolonged period in a microelectronic package is increasingly being sought in such diverse areas as field emission displays (FEDs), micro-electro-mechanical systems (MEMS) and atomic resolution storage devices (ARS) that are used in connection with computers, displays, television sets as a few examples. Both FEDs and ARS typically require two surfaces juxtaposed to one another across a narrow vacuum gap. Typically, electrons must transverse this gap either to excite a phosphor in the case of FEDs or to modify a media to create bits in the case of ARS.
One of the major problems with vacuum packaging of electronic devices is the continuous outgassing of hydrogen, water vapor, and other components found in ambient air from the internal components of the electronic device. This is especially true for polymers such as epoxies and polyimides, which are widely used in the electronic industry. To minimize the effects of outgassing one typically uses gas-absorbing materials commonly referred to as getter materials. Normally the getter material is incorporated into a separate cartridge, which is inserted into the electronic vacuum package. Thus, in order to maintain a vacuum over the lifetime of the electronic device a sufficient amount of getter material must be contained within the cartridge or cartridges before the cartridge or cartridges are sealed within the vacuum package. In addition, connections to or a means of activating the getter material once it is sealed within the vacuum package is also required. Further a path of sufficient cross sectional area to allow for the gaseous material outgassing from various surfaces of the device to impinge upon the surface of the getter material is necessary for efficient pumping action.
In conventional getter cartridges the getter material is deposited onto a metal substrate and then activated using, electrical resistance, RF, or laser power to heat the getter material to a temperature at which the passivation layer on the surface diffuses into the bulk of the material. Non-evaporable getter material is activated in a temperature range of 450-900xc2x0 C. depending on the particular material used. At these temperatures both active devices as well as polymeric materials will be damaged and/or deformed. In order to avoid these damaging effects the getter material must be kept apart from the actual device, thus leading to a bulkier package as well as greater difficulty in assembly. In addition, the incorporation of a separate cartridge, especially for small electronic devices with narrow vacuum gaps, also results in a bulkier package. Further, the utilization of a separate cartridge increases the cost of manufacturing because it is a separate part that requires accurate positioning and then it must be secured to another component part to prevent it from coming loose. Loose cartridges are a potential serious problem by either acting as a source of small particles that break away from the cartridge or create particles from materials the cartridge is in contact with.
An electronic device that is sealed under vacuum includes a substrate, a transistor formed on the substrate, and a dielectric layer covering at least a portion of the transistor. The electronic device further includes a layer of non-evaporable getter material disposed on a portion of the dielectric layer, and a vacuum device disposed on a portion of the substrate. Electrical power pulses activate the non-evaporable better material.